A pressure and/or pressure difference transducer STD 915 from Honeywell is produced according to a method of this type. In the production of this conventional transducer, the separating diaphragm is pre-molded in such a way that it has a pot-like shape with a wide edge. At the inner area of the edge, the separating diaphragm is welded to an inner body of the transducer in an annular shape. Outside the annular weld seam, a sealing ring is provided in the conventional transducer, which lies in an annular groove of a pressure cap and is pressed with the pressure cap against the separating diaphragm on the inner body. Previously, in the production of the conventional transducer, the separating diaphragm was post-molded by pressing it against a structured area of the surface with wave-like elevations and depressions.
An object of the present invention is to provide a method for the production of a separating diaphragm system for a pressure transducer by which a pressure transducer with very good measuring characteristics can be produced.
According to the present invention, an inner body is used, the structured area of which is limited to the outside by an outer wave crest-like elevation. The collar of the pre-molded separating diaphragm is joined on the outside to the outer wave crest-like elevation adjacent to the inner body, following which post-molding of the separating diaphragm is carried out and the pressure cap with the sealing ring is then attached.
An advantage of the method according to the present invention is that a pressure transducer--and of course, a pressure difference transducer as well--can be produced with it, the separating diaphragm being pressed onto the outer flank of the outer wave-like elevation and its "crest" due to the attachment of the collar of the pre-molded separating diaphragm to the outside of the outer wave-like elevation and due to the subsequent post-molding via the initial radial tensile stress which arises and remains in the separating diaphragm. As a result, the fixation diameter of the separating diaphragm is precisely defined and hardly changes even with pressure fluctuations. Accordingly, the volume stiffness of the separating diaphragm stays nearly constant even with changes in pressure.
In one example embodiment of the method according to the present invention, the collar on the outer flank of the outer wave-like elevation is joined to the inner body. In this manner, it is possible to obtain a pressure transducer having a relatively compact structure.
Moreover, in order to obtain a pressure transducer with a precisely defined fixation diameter of its separating diaphragm, it may be advantageous if the collar is joined to the inner body in an area of the elongated flank of the outer wave-like elevation lying below the level of the wave-like depressions.
In a further example embodiment of the method according to the present invention, the separating diaphragm is pre-molded in such a way that on its outer edge it has a flat annular area adjoining the collar. The flat annular area of the separating diaphragm is joined to a flat edge of the inner body.
If a pressure transducer is to be produced for corrosive media, the sealing ring is arranged so as to cover the connection point between the separating diaphragm and the inner body.
An additional object of the present invention is to provide a separating diaphragm system for a pressure transducer which provides the pressure transducer with very good measuring characteristics.
In order to achieve this object, in a separating diaphragm system for a pressure transducer with an inner body having a structured area on its outer surface with annular, wave crest-like elevations and annular, wave trough-like depressions, with a separating diaphragm having a collar formed by premolding in the area of its outer circumference. The separating diaphragm is fixedly joined to the inner body so as to be gas-tight via an annular connection point on the collar and is correspondingly corrugated by post-molding the outer surface of the inner body. An outer pressure cap is pressed against the separating diaphragm with interposition of a sealing ring. According to the present invention the structured area of the inner body is limited to the outside by an outer wave crest-like elevation and the collar of the separating diaphragm is joined to the outside of the outer wave crest-like elevation adjacent to the inner body.
A separating diaphragm system is described in U.S. Pat. No. 4,199,991 in which an inner body of a pressure transducer has in the vicinity of its edge on its outer surface a structured area with an annular wave crest-like elevation and an annular wave-like depression and a separating diaphragm is attached to the edge of the outer surface of the inner body via an annular welding seam. The separating diaphragm is corrugated corresponding to the outer surface of the inner body. A pressure cap is pressed against the separating diaphragm, the pressure cap accommodating a sealing ring at the edge of an inner recessed area. However, the conventional separating diaphragm system does not have a pre-molded collar. Also, the structured area of the inner body is limited to the outside by a wave trough-like depression. The conventional separating diaphragm system prevents corrosive media that may be present in the pressure cap from attacking the inner body. The inner body is in fact completely sealed off from the medium in the pressure chamber by the separating diaphragm and the sealing ring. Therefore, it is not necessary to use material resistant to corrosive media for the inner body, which provides a cost benefit in manufacturing and moreover does not pose any significant problems in welding the separating diaphragm to the inner body.
Another advantage of the separating diaphragm according to the present invention is that as a result of its design, the fixation diameter of the separating diaphragm is defined relatively precisely and does not vary even with pressure fluctuations within a pressure transducer. If, for example, the pressure cap expands due to a change in pressure, the fixation diameter of the separating diaphragm in the separating diaphragm device according to the present invention is not influenced to any great extent because it is fixed by the "crest" of the outer wave crest-like elevation. This may be important because the fixation diameter of a separating diaphragm has a very great influence on the spring properties of the separating diaphragm and accordingly on the measuring characteristics of a pressure transducer. Thus, the separating diaphragm system according to the invention does not disadvantageously change the measuring characteristics.
In the separating diaphragm system according to the present invention, the connection point between the separating diaphragm and the inner body is located outside and below the outer wave crest-like elevation and below the "crest" of this elevation. This can be achieved in that the outer flank of the outer wave crest-like elevation is elongated to below the level of the wave trough-like depressions and the connection point between the separating diaphragm and the inner body is located in the elongated area of the outer flank. In this case, even severe expansions of the pressure cap caused by high pressure changes do not bring about a noticeable change in the fixation diameter of the separating diaphragm.
In an additional example embodiment of the separating diaphragm system according to the present invention, the separating diaphragm has at its outer edge a flat annular area adjoining the collar, the flat annular area of the separating diaphragm being joined to a flat edge of the inner body.
In order to prevent corrosive media in the pressure chamber from possibly gaining access to the connection point, in an advantageous manner in the separating diaphragm system according to the present invention, the sealing ring is arranged so as to cover the connection point.